An air lock device is used to gravity dry, free-flowing materials from one pressure zone to another. It is used, for example, to transmit material from an overhead collection point to a pressurized pneumatic conveying system pipeline without employing boiler flue gases as a conveying medium and without causing reentrainment of the material into the gas stream.
The air lock device includes a valve which isolates a bottom vessel from an upper vessel and a valve which isolates the bottom vessel from the conveying pipeline. Another valve on the upper vessel controls the introduction of materials thereinto. When materials are introduced into the upper vessel, the upper vesel must be vented to atomosphere so as to permit air to escape. Material is discharged from the upper vessel to the lower vessel by introducing a gas into the upper vessel at an elevation above any materials therein and at a pressure greater than the pressure of the conveying pipeline.
It is necessary to provide the air vent with a filter system to preclude the escape of high temperature dry, free-flowing materials. The problem is to prevent such discharge of materials to the surrounding atmosphere or into other parts of the system while at the same time having a filter element which requires little or no maintenance, can withstand the temperatures involved, and is readily accessible while at the same time will permit flow in opposite directions.